The present invention relates to railroad freight cars, and particularly to a multi-unit railway freight well car of lightweight construction, for optionally carrying either intermodal cargo containers stacked one upon another or over-the-highway freight trailers supported on their own running gear in a cargo well of any car unit of the multi-unit car.
Railroad car units for carrying over-the-highway freight trailers are well known, as are multi-unit railroad freight cars defining cargo or container wells for carrying various combinations of intermodal cargo containers stacked one upon another in two tiers. Because the total weight which can be carried upon the rails limits the net amount of cargo which can be carried on a railroad freight car unit, it is desirable for a well car unit to be constructed in a configuration having a minimum tare weight consistent with the strength required to safely support a combination of cargo containers and trailers for which the car unit is configured. It is also necessary, however, to provide an adequate surface to support the tires of trailers carried in the cargo well. Additionally, it is necessary for a car unit to be strong enough to withstand the many forces resulting from movement of the laden car unit as part of a train.
Some highway freight trailers are longer than the cargo wells commonly provided for receiving stacked containers in the car units of such multi-unit well cars, but it is preferred not to build car unit bodies with longer wells to accommodate such trailers because of the limitation of cargo capacity resulting from the extra weight of such a longer car unit body. Nevertheless, it is desired to be able to carry such longer trailers safely in such multi-unit well cars. At the same time, it is desirable to provide in a railroad freight car the ability to carry a widely variable mix of containers and trailers of various sizes, and thus to minimize the number of spaces for trailers or containers left empty in loading the car units of a train.
To carry trailers efficiently in a well car unit it is necessary to provide a shallow well depth from a floor top surface to the top of a side sill, to give trailer loading equipment access to the bottom of a trailer floor above the side sills so that trailers can handily be inserted into and extracted from the well. The reduction of bending resistance resulting from shallower side sills must be restored by other structure.
Well car units utilize inter-box connectors (IBCs) to interconnect upper and lower containers when they are carried stacked one atop another in a well car unit. IBCs are usually located at a standard position between such stacked containers, corresponding to the location of an end of a standard intermodal container 40 feet long, for example, even though it is possible that a container more than 40 feet long may be carried.
It is necessary for a person to reach the IBC to operate it to interconnect or disconnect containers when a container is being loaded onto or removed from atop a lower tier container carried in a well of such a car unit. Since some containers are over 9' high, it may be difficult to reach the IBCs when standing atop a side sill of a well car unit, particularly one which has relatively low side sills. There is additional risk of falling where a well car unit is intended to carry containers having lengths greater than 40 feet. Some car units for carrying stacked containers therefore include walkways on which a person can stand to reach IBCs.
Some railroad freight car units are designed to carry trailers, or chassis and attached intermodal cargo containers, in a cargo well also equipped to carry stacked containers. The structure of such well car units must satisfy certain requirements. First, any walkways intended to provide access to IBCs interconnecting stacked containers carried in such a car unit should be located where they will not interfere with the proper operation of cranes used to move trailers into or out of such car units.
Second, it is necessary for the car unit structure to carry loads, imposed upon the car unit by the weight of containers or trailers, from the side sills to the wheeled trucks supporting the car unit. However, such loads are concentrated in the side sill structure of the car unit near the ends, because of the need for clearance for the wheeled trucks to pivot.
What is needed, then, is an improved multi-unit railroad car including cargo wells for optionally carrying either stacked containers or trailers of various lengths, including trailers longer than the cargo well in a car unit, yet without restricting availability of the cargo well of an adjacent car unit, and in which a well floor structure and the connection of such a well floor to other parts of the car provide adequate strength without unnecessary weight, yet with shallow well depth and small floor thickness, and in which provision is made for a person to reach and operate inter-box connectors safely when containers are stacked in the cargo well.